The present invention relates to a sensor device including a sensor that transmits radio waves at a predetermined frequency and receives reflected waves of the radio waves, detects a moving body based on a difference of the frequency of the radio waves and the frequency of the reflected waves to activate a light source.
Japanese Laid-Open Patent Publication No. 2001-124187 describes an example of a lighting device that uses a sensor to detect the presence of a human body in a detection area and activates or deactivates a light source in accordance with the detection. One such sensor is an active type sensor that transmits detection waves, such as electromagnetic waves, and receives the detection waves reflected by an object to detect the presence of a moving body in a detection area.
When two lighting devices are arranged opposing each other, the sensor of one lighting device transmits radio waves having an oscillation frequency that differs greatly from that of the radio waves transmitted from the sensor of the other lighting device. This reduces the interference of the radio waves from the sensors.
In an active type sensor, light sources proximal to the sensor may interfere with the radio waves. In such a case, even though a moving body is not present in the detection area, the active type sensor may determine that a moving body is present in the detection area, and thereby, erroneously activate a light source. In particular, when two lighting devices are in an opposing arrangement, sensors of the two lighting devices may be activated at the same time. In such a case, a difference in the oscillation frequency of the radio waves transmitted from the sensor of one lighting device and the oscillation frequency of the radio waves transmitted from the sensor of the other lighting device may be detected as a Doppler frequency shift.